Electrodeposition apparatus



Oct. il, 1949. J. M. Boos-z 2,48%068 ELECTRODEPOSITION APPARATUSOriginal Filed March 1l, 1943 2 Sheets-Sheet 1 lli sum-wf 10/ INVENToR.Kawai Marzfmwe Oct. 1l, 1949. J. M. 4BboE 2,484,068

ELECTRODEPOSITION APPARATUS Original Filed March l1, 1943 2-Sheets-Sheet 2 l INVENTOR.

.fd/4ms Murwhwe BY MTM Patented Oct. 11, 1949 corporation of. DelawareOriginal application March .lames M. Bone, lndianapolis, Ind., assignerto P. R. Mallory & Co.,

lne.,v Indianapolis,- Ind., a

11, 1943', Serial No.

478,750.. Dividedy and this application March` 10, 1944,.Serial No.525,907

'Claims. 1

This invention relates to apparatus for the electrodeposition of metalsand alloys. This application is a .division of my co-pending applicationS. N. 478,750 filed March 11, 1943.

An object of the invention is to improve electrodeposition apparatus.

Other objects of the invention will be apparent from the description andclaims.

In the drawings:

Figure 1 is a diagram illustrating the preferred Working range of anodecurrent density for electrodeposition according to the presentinvention;

Figure 2 is an elevation with parts in vertical section showing aplating tank and apparatus for plating the inside of a cylinder;

Figure 3 is an elevation with parts in vertical section ofelectroplating apparatus showing the use of two anodes and two powersources for alloy plating;

Figure 4 is an elevation of a tank plating apparatus using a singlepower source;

Figure 5 is a longitudinal section of an anode for alloy plating;

Figure 6 is an elevation partly in section of part of an electroplatingapparatus showing a modified anode feeding arrangement for alloyplating; and

Figure 7 is an elevation partly in section showing another anode feedingarrangement.

The present invention contemplates the use of tapered or pointed anodesand of improved mounting arrangements and means for introducing theanodes into the electrodeposition bath.

In the electrodeposition of metals and alloys I have found that theanode surface condition can be changed by increasing the anode currentdensity. Various anode surface conditions are indicated in the diagramof Figure 1. With low anode current densities the anode takes on acrystalline, matte, or dull, appearance. Plating processes of theV priorart operated the anodes in this range. This has resulted in metalparticles falling into the solution. In this range, the current isroughly proportional to the applied voltage. The black anode condition,if present, occurs in this range.

As the voltage is increased, aA point A is reached where the anoderather suddenly becomes smooth and bright and is no longer crystallinein appearance. This may be accompanied by fluctuating shadows playingover the anode surface. It is also accompanied by a sudden rise involtage at the anode without a proportional rise in current. Furtherincrease in voltage will not proportionally increase the currentdensity. The anode may be said to be in a semi-polarized condition.Dissolution appears to take place uniformly over the anode surface.

The semi-polarized range has asits upper limit B the current density atwhich the anodeV becomes completelyv polarized asf evidenced" by for- 2mation of an insoluble dull coating on the anode surface or generationof gas.

The type of behavior described above applies to the platable metals,generally, that is, to Zinc and the metals below it in theelectrochemical series, such as cadmium, iron, the tin group, lead,copper, silver, gold, the, platinum group and others, as well as toalloy anodes. The current densities A andB, marking the limits of thesemipolarized range, depend upon the anode metal as well as upon thecomposition of the plating bath, the temperature and therate of.circulation or agitation of the bath.

I have found that by operating the anode in the semi-polarized range theplating diiculties associated with flne metal particles inthe bath canbe eliminated and. other advantages attained as well. Not. only are no.particles of the anode metal released into the bath,` but the impuritiesassociated. with black anodes do not form particles in the solution. Inthe bright range apparently the oxidizing potential is sufficient todissolve the impurities along with the silver so that no precipitateforms` at the anode.

With ordinary alkaline plating baths, the bright range A--B is narrow.and. occursV at a fairly low current density. The current density forthe bright range can be increased and the bright range broadened by theaddition of corrosive ions to the plating bath. These. are ions whichform highly soluble compounds with the anode metal and hencepromotedissolution of. the anode. For example, in. the case of aleadanode tartrate and citrate ions produce this result and hence theaddition of one of. their compounds, such as p0- tassium tartrate,isfdesirable. With silver anodes cyanide is a corrosive ion.

When. operated. inA the. brighty range with corrosive ions present theanode, operates at current eniciency.

Increase in temperature, of theplating bath and increased. circulation`or agitation also raise and broaden the bright range and so are. alsodesirable for better regulations,- higher plating speeds and greaterefliciency.

In raising the anode current'density the-anode size isvrcduced for a.given cathode area. It has been conventional in electropla-ting practiceto provide ananode area at least. equal to thecath'- ode area andusuallyl greater than the cathode area. This was done;beca-usewithsmaller anode areas, under us-ualt platinge conditions,gassing takes place at the' anode, causing a depletion of metal` in thebath;v andA in the case of' cyanide baths, acceleration of the formationof car'- bonates; In the presentinvention. the anode area is greatly'reduced; In; they case: of lead. anodes, for example', the? anode: area.may be only 1/30 to 1/ 1u thatv of the'- cathodey and the7 anode currentdensity may'beni toioiajmperes per square foot.

The small anode area also introduces mechanical advantages in platingcertain shapes.

In summary, the following factors are combined to provide anelectrodeposition process which prevents the introduction orf-,metalparticles into the solution, operates at greater plating speed and has100% anodecurrent efficiency;

1. Operation of anode in'semi-polarized or bright range.

2. Use of corrosive ionsin the plating bath. This is particularlyapplicable to alkaline baths.

3. Operation at high anode current density.

4. Anode area much smaller than cathode area.

The anode area in contact with the solution is small, and it must bekeptwithin certain fairly close limits-in order to preserve thesemipolarized condition 'and 'toregulate the cathode current density. Ihave devised an anode rod havinga body portion of substantially uniformcross section'and an end'portion ytapered to a point, which is allowed-to rest on a support in the plating bath. If the semi-polarizedcondition is maintained along with fairly uniform agitation of the bath,the anode will dissolve uni-- formly and asharply pointed lcondition i-spreserved and the anode settles so as to keep the same area always inthe solution. This will be clearer from the more detailed descriptionand the illustrations of the drawings.

Plating apparatus suitable for plating a single metal, such as lead,silver or copper is illustrated in' Figure 2 of the drawing andcomprises a tank I containing the plating bath II, the anode I2 which istapered to a point I3 which rests on a perforated insulating plate I 4,the cathode I5 comprising a bearing sleeve resting on plate I4, aninsulating tubular mask I6 surrounding the exterior of the cathode, anda circulating pump I'I. A covered conductor I8 passes through mask I6and connects the cathode to the negative terminal of a D. C. powersource. The pump I'I is driven by electric motor I 9 and draws inplating solution at and forces it via pipe 2I through the holes in plateI4 and up through the center of the cathode bearing shell I 5.

The anode I2 comprises a rod of lead, silver, copper or other metal(preferably round) having a body portion of substantially uniform crosssection which is tapered to a point I3 at its lower end. 'I'he taper isof such length as to provide the desired anode area in the taperedsection. The support for the point I3 and the solution level areadjusted to bring the surface of the solution even with the `upper endof the taper.

The anode rod is supported loosely by an insulating sleeve 22 above thesoltuion so that it may settle into the solution as the tapered portionis dissolved.

I have found that under these conditions, when the anode is operated inlthe'bright or semipolarized condition, and the circulation or agitationof the solution around the anode is fairly uniform, the current isuniformly distributed over the entire tapered area so that the taperedsurface dissolves uniformly from the beginning of the taper to the tip,thus the same taper is p always preserved as the anode rod settles intothe solution and no particles or sections can become eaten away from theanode and drop olf into the solution. f

Figure 3 shows a suitable apparatus for silverlead plating. -Itcomprisesplating tank containing silver-lead bath 3I, silver anode 32,lead `anode 33, cathode 34 and vcirculating pump 35 driven by motor 36.Both the lead anode 33 and the silver anode 32 have body portions ofsubstantiallynniform cross section and are tapered,

the tapered surfaces being proportioned to the relative areas required.Silver anode 32 rests on perforated plate 31 so that its tapered portionis located along the axis of the cathode cylinder. The lead anode 33rests on an insulating table 38 outside the cathode. The silver anode isconnected to D. C. source 39 through current regulating resistance 40and the lead anode is connected to D. C. source 4I through regulatingresistance 42. It is thus possible to adjust both anode currentsindependently.

Figure 4 shows a plating apparatus suitable for tank plating ofmiscellaneous parts. It comprises a tank 43 containing plating bath 44,tapered anodes 45 and 46, having body portions of substantially uniformcross section, and cathode 4'I. The bath is agitated by a stirrer 48driven by motor 49.

The anodes rest their pointed tips or insulating supports below thesolution level and slide into the solution through guiding sleeves 56and 5I of insulating material. The cathode parts are suspended by hooks52 from bus bar 53 connected to the negative terminal of a D. C. source54. The anodes 45 and 46 are connected to the positive terminal of thesource through current regulating adjustable resistors 55 and 56respectively. The current can thus be readily proportioned between theanodes.

The anodes may be of the same or different composition depending uponWhether pure metal or an alloy is to be deposited, the plating bathbeing of suitable composition.

It is also contemplated that in the arrangements of Figures 2 and 4 theanodes can be formed of an alloy of the composition to be deposited. Theoxidizing potential, when the anodes are operated in the bright range,is suilicient to dissolve both metals simultaneously.

Figure 5 shows in section a tapered anode, having a body portion ofsubstantially uniform cross section, for alloy plating comprising a core6I of a rst metal and a coating 62 of the second metal to be deposited.For example, the core may be of silver and the coating of lead. Theanode is supported from the silver tip 63 in the plating bath with thelevel of the bath at the upper end of the taper 64. With corrosive ionsfor both metals in the solution, it is possible to operate the anodewith both metals working in the bright range so that uniform dissolutiontakes place and the same taper is preserved as the anode settles intothe bath. With a silver-lead anode there is some tendency of the lead topolarize due to the high current density but this can be overcome byusing sufficiently high pH solutions. The thickness of the metal coating62 is selected to give a relative cross-section of the two metals in theproportions desired in the electrodeposited alloy.

Figure 6 shows a modification in which the two tapered anodes 65 and 66,having body portions of substantially uniform cross section, are

clamped in an insulating yoke 61 at their upper ends and the point ofanode 65 rests on table 68 under the solution and is guided by loosesleeve guide 63. It will be apparent that dissolution of both anodeswill take place at the same linear rate and hence the amount of themetals dissolved will bein proportion to their areas.

Figure '7 shows a method of introducing a tapered anode, having a bodyportion of substantially uniform cross section, below the surface of theplating bath. The

plating tank is provided with a circular aperture 15, the edge of whichis lined with a soft rubber or a synthetic elastomer, for examplepolymerized chloroprene ring ll through which anode 'l2 is fed by aspring 13 or other feeding means. A stop 'lll in the bath maintains thesame tapered length in solution as the anode dissolves.

While specic embodiments of the invention have been described7 it isintended to cover the invention broadly within the spirit and scope ofthe appended claims.

What is claimed is:

1. In an apparatus for the electrodeposition of metal from a bath, thecombination which comprises an anode in the form of a rod composed ofthe metal to be deposited, said rod having a body portion ofsubstantially uniform cross section and an end portion tapered to apoint, means for slidably supporting the body portion of said rod, asupporting plate for the point of said rod, and means for urging thepoint of said rod against said plate, said supporting means and platebeing so constructed and arranged as to expose solely the tapered endportion of the rod to contact with the bath.

2. In an apparatus for the electrodeposition of metal from a bath, thecombination which comprises a cathode, an anode rod of the metal to bedeposited having an elongated body portion of substantially uniformcross section and an end portion tapered to a point and in contact withthe bath, the surface area of said tapered portion being the effectiveanode surface area and being only a small portion of the effectivecathode area, a sleeve for` holding the body portion of the rod forsliding axial displacement, a support in the bath, means for urging the`point of the rod against said support, said urging means and saidsupport cooperating to advance the rod into the bath at substantiallythe same rate as is dissolved and to retain a substantially uniformtapered shape having a substantially uniform surface area.

3. In an apparatus for the electrodeposition of metal from a bath, thecombination which comprises a tank for the bath having an aperture in awall thereof below the level of the bath, an anode rod having a bodyportion of substantially uniform cross section and an end portiontapered to a point extending through said aperture, a sealing sleeve insaid aperture around said anode rod, a stop in said tank at the point of`said rod, resilient means urging said point against said stop, and acathode in said tank whereby, upon the application of a predeterminedpotential difference to said cathode and anode, metal will be depositedon the cathode and metal will be dissolved from the tapered portion ofthe anode rod and the said rod will be progressively fed into the bathat the same rate as it is consumed while retaining a tapered shape atits end.

4. In an apparatus for electroplating the inner surface of a cylinder,the combination which comprises an electroplating tank for holding aplating bath, means for supporting the cylinder to be plated in saidtank with its axis vertical to and below the level of the bath, anelongated anode rod formed of the metal to be plated having a bodyportion of substantially uniform cross section and having one of its endportions tapered to a point, means for holding said rod for slidingdisplacement along the axis of said cylinder, and a support in said tankupon which the point of the anode rod rests with its tapered end portionin -contact with the bath said holding means and said support being soconstructed and arranged that, upon the application of a predeterminedpotential diiference between said cylinder and lsaid rod, metal isdeposited upon said cylinder and metal is dissolved from the taperedportion of said rod and the said rod is fed progressively by gravityinto the bath at substantially the same rate as it is consumed whileretaining its tapered shape at the end.

5. In an apparatus for the codeposition of metals from a plating bath,the combination which comprises a pair of anode rods formed respectivelyof the metals to be codeposited, each of said rods having an elongatedbody portion of substantially uniform cross section and an end portiontapered to a point, a stop in the bath against which the point of therst one of the rods may abut, continuously effecting feeding means formaintaining the point of said rod on said stop in such position as toexpose solely the tapered end portion of the rod to contact with thebath, means securing the second of Isaid rods in xed parallel relationto said first rod with its tapered portion exposed to contact with thebath, and a cathode in the bath whereby, upon the application of apotential difference to said anode rods and cathode, an alloy will bedeposited upon the cathode and metal will be dissolved from the taperedportion of both anode rods and the said rods will be progressively fedat the same linear rate into the bath While retaining a tapered shape attheir ends.

6. In an apparatus for the electrodeposition of metal from a bath, thecombination which comprises an anode rod composed of the metal to bedeposited having a body portion of substantially uniform cross sectionand an end portion tapered to a point, means for holding the bodyportion of said rod for sliding displacement in generally perpendiculardirection, and a supporting plate for the point of said rod againstwhich said point is urged as a result f the action of gravity on therod, said supporting means being so constructed and arranged as toexpose solely the tapered end with the bath.

JAMES M. BOOE.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS portion of the rod to contact Number Name Date485,537 Edwards Nov. 1, 1892 542,057 Hulin July 2, 1895 578,070 WoolfMar. 2, 1897 858,160 Deloye June 25, 1907 1,017,671 Jenkins Feb. 20,1912 1,022,487 Lutz Apr. 9, 1912 1,043,937 Huth Nov. 12, 1912 1,077,920Stevens Nov. 4, 1913 1,280,249 Landry Oct. 1, 1918 1,435,671 StewartNov. 14, 1922 1,565,683 Swain Dec. 15, 1925 1,839,931 Reppen Jan. 5,1932 1,851,789 Ward Mar. 29, 1932 1,861,446 Maag June 7, 1932 2,046,467Krause July 7, 1936 2,048,578 Van der Horst July 21, 1936 2,086,224I-Ienrioks July 6, 1937 FOREIGN PATENTS Number Country Date 790,074France Nov. 12, 1935

